1. Technical Field
The present invention relates to an ink set, and to an ink jet recording apparatus and a recorded article that use the ink set.
2. Related Art
An ink jet recording method is a technique for printing, and in which printing is performed by ejecting ink droplets so as to be deposited on a recording medium, such as a paper sheet. The ink jet recording method is being innovatively developed and increasingly applied to the application of high-resolution image recording (printing) which has been performed by photo printing and offset printing. Accordingly, it is desired that high-quality images be recorded not only on general plain paper and ink jet recording paper (matte paper, glossy paper), but also on other recording media, such as book printing paper, synthetic paper, and films.
Dyes and pigments are used as coloring agents, and, in particular, water-soluble dyes are often used in color inks because of their chromaticness, transparency, solubility in water and other properties. However, water-soluble dyes are generally inferior in light fastness and gas fastness. In addition, their water fastness is not good because water-soluble dyes are soluble in water. Accordingly, recorded articles produced with an ink containing a water-soluble dye are inferior in storage. In contrast, coloring agents insoluble in water are advantageous in terms of water fastness. Among coloring agents insoluble in water are pigments. Pigments are superior in light fastness, gas fastness, and water fastness. Accordingly, pigment inks exhibiting such properties of the pigment are being developed.
On the other hand, aqueous pigment inks for ink jet recording are simultaneously required to have high color developability and glossiness, to exhibit a small degree of bleeding and such an ejection stability as ejection from head nozzles does not veer, and to be stored stably.
However, if the pigment content in an ink is increased to enhance the color developability, the viscosity of the ink is increased, and the anti-clogging properties, ejection stability, and storage stability of the ink are degraded. In addition, if the penetration of the ink is enhanced in order to prevent bleeding or increase printing speed, the ink undesirably penetrates into the recording medium and is thus unlikely to remain on the surface of the recording medium. This causes the degradation of the uniformity and color developability of images filled with a solid color.
Accordingly, in order to enhance printing quality (color developability, anti-bleeding properties, uniformity of solid color area) and reliability (storage stability, printing stability), JP-A-2009-235155 proposes that a glycol ether having a hydrophile-lipophile balance (HLB) value, measured by Davies method, of 4.2 to 8.0 and an 1,2-alkanediol be added to an ink.
This technique, however, degrades the storage stability of some of the known inks, depending on the combination of the coloring material (type of pigment) and glycol ether used in the ink. Also, the quality of images printed on non-absorbent recording media, such as films, has not been studied.